The invention relates to an amplifying circuit for amplifying an audio reproduction signal or the like including frequency components in a range from a low frequency to a high frequency.
In recent years, the size and weight of portable audio devices have been more and more reduced, and the realization of a high fidelity (Hi-Fi) audio apparatus is required together with the realization of a small size and a small electric power consumption from a battery.
To meet the above requirements, for instance, a conventional amplifying circuit is constructed as shown in FIG. 1.
In the diagram, when a reproduction signal is supplied from an input terminal 22, the reproduction signal is amplified having an amplifying circuit 21 by an amplification gain which is determined by gain setting resistors 24 and 25. After that, the amplified signal is generated from an output terminal 23 through a coupling capacitor 26 and a resistor 27. In such a conventional amplifying circuit 21, as shown in FIG. 2A, an input signal M of the amplifying circuit 21 is amplified within a range of an output dynamic range D as shown in FIG. 2A.
However, such a conventional amplifying circuit has a problem such that in the case of amplifying a signal of, particularly, a music source having frequency components in a range from a low frequency to a high frequency, as shown in FIGS. 2A and 2B, despite the fact that a power source voltage d exists, the amplifying circuit has only an output dynamic range D from which a circuit using region C has been subtracted. As a result, when a sound volume is raised, as shown in FIG. 2B, a high amplitude portion of the amplified signal reaches the upper or lower limit of the output dynamic range D and is distorted.